Shell Script Error Handling with set and trap

Shell scripts silently continue after errors, leaving systems in inconsistent states. Failed commands go unnoticed until much later.

Robust shell script template:

#!/usr/bin/env bash
set -euo pipefail
IFS=\n\t'

# -e: Exit on error
# -u: Error on undefined variables
# -o pipefail: Pipe fails if any command fails
# IFS: Safer word splitting

# Cleanup on exit (success or failure)
cleanup() {
  local exit_code=$?
  echo "Cleaning up..." >&2
  rm -f "$TEMP_FILE" 2>/dev/null || true
  return $exit_code
}
trap cleanup EXIT

# Error handler with line number
on_error() {
  echo "Error on line $1, command: $2" >&2
}
trap 'on_error $LINENO "$BASH_COMMAND"' ERR

# Safe temp file
TEMP_FILE=$(mktemp)

# Handle expected failures
if ! grep -q 'pattern' file.txt; then
  echo 'Pattern not found' >&2
  # Don't exit - this is expected
fi

# Or use || true for commands that may fail
rm -f optional_file.txt || true

Without set -e, a failed command in the middle of a script is silently ignored. The script continues with stale or missing data, potentially causing data corruption or deployment failures.

Writing reliable shell scripts